Prevalence and aetiology of neuropathic pain in cancer patients: a systematic review.

Pain in cancer patients remains common and is often associated with insufficient prescribing of targeted analgesia. An explanation for undertreatment could be the failure to identify neuropathic pain mechanisms, which require additional prescribing strategies. We wanted to identify the prevalence of neuropathic mechanisms in patients with cancer pain to highlight the need for detailed assessment and to support the development of an international classification system for cancer pain. We searched for studies that included adult and teenage patients (age above 12 years), with active cancer and who reported pain, and in which a clinical assessment of their pain had been made. We found 22 eligible studies that reported on 13,683 patients. Clinical assessment methods varied, and only 14 studies reported confirmatory testing for either sensory abnormality or diagnostic lesion to corroborate a diagnosis of neuropathic pain. We calculated that the prevalence of patients with neuropathic pain (95% confidence interval) varied from a conservative estimate of 19% (9.4% to 28.4%) to a liberal estimate of 39.1% (28.9% to 49.5%) when patients with mixed pain were included. The prevalence of pain with a neuropathic mechanism (95% confidence interval) ranged from a conservative estimate of 18.7% (15.3% to 22.1%) to a liberal estimate of 21.4% (15.2% to 27.6%) of all recorded cancer pains. The proportion of pain caused by cancer treatment was higher in neuropathic pain compared with all types of cancer pain. A standardised approach or taxonomy used for assessing neuropathic pain in patients with cancer is needed to improve treatment outcomes.